Multilayer hard coating for tools

ABSTRACT

A multilayer hard coating for tools for machining applications with a multilayer structure for improving the wear resistance of workpieces includes at least one (Al y Cr 1-y )X layer (0.2≦y≦0.7), wherein X is one of the following elements N, C, B, CN, BN, CBN, NO, CO, BO, CNO, BNO, CBNO, but preferably N or CN, and/or a (Ti z Si 1-z ) layer (0.99≧z≧0.7). The hard coating also includes at least one layer stack with one (AlCrTiSi) X mixed layer, followed by another (Ti z Si 1-z )X layer, followed by another (AlCrTiSi) X mixed layer, followed by another (Al y Cr 1-y )X layer.

TECHNICAL FIELD

This invention concerns a multilayer hard coating for tools (hard metaland high-speed steel) for machining applications—especially drillingapplications.

-   1a) Tools coated with hard coatings, with a series of several    different aluminum chromium nitride or carbonitride and titanium    silicide nitride or carbonitride layers-   1b) Tools, especially cutting and forming tools (drills, millers,    taps, formers, roller cutters, stamps, dies, drawing stamps, etc.)    with a series of several different aluminum chromium nitride or    carbonitride and titanium silicon nitride or carbonitride layers and    the use of such tools-   1c) A method of producing a series of several different aluminum    chromium nitride or carbonitride and titanium silicon nitride or    carbonitride layers with a defined layer structure.

STATE OF THE ART

EP 1174528 A2 describes a tool coating comprised of a series of severalindividual layers, wherein the first layer is composed of a nitride,carbide, carbonitride, boride, oxide, etc. of the elements Ti, Al and/orCr, and a second layer is composed of a nitride, carbide, carbonitride,boride, oxide etc. of Si and at least one element from groups 4a, 5a and6a of the PTE [Periodic Table of the Elements]. The advantage of thiscoating is that the Si in the upper layer critically improves the wearresistance and oxidation resistance. The Cr—Si-based cover layers mainlyimproved tool life. TiAlN, CrAlN and TiN layers are chosen for thebottom layer.

EP 1422311 A2 describes Al—Cr—(Si)—O-based hard layers that can be madeas nitrides, carbide, oxide, boride, etc. For all layers, it is truethat a small percentage of oxygen (1-25%) is contained in the layers. Itshould also be mentioned that another hard layer can be applied in thecoating mentioned in the invention. Ti—Si—N Ti—B—N, BN, Cr—Si—N, etc.,inter alia, are given here as examples. One advantage of the inventionis the use of small quantities of oxygen or silicon and oxygen, sincethis results in greater hardness, improved wear resistance andhigh-temperature oxidation resistance.

EP 1219723 A2 introduces a Ti—Al—Cr—X-N-based coating, where X can standfor Si, B and/or C. The advantage of this coating is to improvewear-resistance compared to conventional coatings. The invention alsodescribes a target that must be composed of at least Ti, Al and Cr.

DISADVANTAGES OF THE STATE OF THE ART

The tools with hard coatings in the state of the art (Ti—Al—N-basedcoatings) have shorter tool lives than the new optimized(Al_(1-x)Cr_(x)X)—Ti_(1-y)Si_(y)) X-hard coatings for X=N or CN.

The disadvantages of the state of the art are also that with Al—Cr—Ncoatings at high temperatures in an atmosphere of inert gas (forexample, an argon atmosphere), the coating starts to decompose at around900° C. If this heat-treatment process is carried out in an atmosphereof oxygen, the decomposition process goes into a higher temperaturerange. Now, if a continual cut is being considered in machining, thelocal temperatures are very high (sometimes over 1000° C.) in thecontact area between the surface of the tool and the workpiece. If thiscontact surface is large enough so that no/little oxygen can have astabilizing effect on the coating surface, the cubic CrN breaks downinto hexagonal Cr₂N and then at a higher temperature into metallic Cr.This coating decomposition process results in premature wear on thecoating in use, which manifests as crater wear in particular.

Problem of the Invention

The purpose of the invention is to prevent the disadvantages of thestate of the art and especially to improve the tool life of coatedtools, like chip removal tools, for example, cutting and forming toolsand components for machinery and forming. It is also the problem of theinvention to provide a method of cutting such coatings, especiallycutting such coatings on sawn workpieces.

Solution or Path to Solution

The invention describes a special multi-layer design for a coating toprevent the coating from disintegrating too fast (wearing out) duringuse. The multi-layer design prevents or at least delays thedisintegration and subsequent diffusion of the Cr—N portion in the AlCrNcoating at high temperatures.

An RCS-type industrial coating system from the Balzer Company is usedfor the deposition of the Al—Cr—(X)—N/Ti—Si—N hard layers, as described,for example, in EP 1186681 in FIGS. 3 to 6 and the Description, column7, line 18 to column 9, line 25. For this, the cleaned workpieces,depending on their diameter, attached to two or, for diameters smallerthan 50 mm, to three rotating substrate holders and two Ti—Si targetsproduced by fusion metallurgy and four targets made of Al—Cr—(X) alloysproduced by powder metallurgy are installed in six cathode arc sourcesplaced on the walls of the coating system. The geometry of the targetlayout is basically determined by the octagonal plot of the RCS system,in which two heating segments arranged opposite each other separate twogroups of three segments in a row with an arc cathode. For theseexperiments, an SiTi target was installed in the opposite middle elementof each group of three. But other target layouts are also possible toproduce such layers. In principle, such layers can be deposited in eachsystem that has at least two arc cathodes in a geometrically equivalentposition, for example at the same coating height of one or more rotatingsubstrate holders. An expert knows it is possible to further influencethe thickness of the individual layers or laminates by arranging thetarget or setting the respective substrate movement or rotation or theangular speed of rotation of a workpiece, depending on the type ofsystem.

Next, the workpieces are brought to a temperature of approximately 500°C. by radiational heating also placed in the system and then the surfaceundergoes etch cleaning by Ar ions by applying a DC bias voltage of −100to −200 V in an Ar atmosphere at a pressure of 0.2 Pa.

After that, an Al—Cr—N adhesive layer approximately 0.2 μm thick isdeposited by operating four Al—Cr sources with a capacity of 3 kW andapplying a substrate bias of −50 V for a period of approximately 5minutes. Then, a multilayer coating is purposely created, in which first2 Ti—Si sources also with 3 kW are connected to the 4 Al—Cr sources, andthey are operated together for a period of approximately 1 minute. Thenthe 4 Al—Cr sources are turned off and a pure Ti—Si—N coating isdeposited for approximately 3 minutes. Then the 4 Al—Cr sources areconnected to it again for approximately 1 minute. After that, the TiSisources are turned off, and a pure Al—Cr—N coating is deposited foranother 5 minutes. This sequence for the layer stack is followed severaltimes during the deposition in the invention. Finally, another coverlayer approximately 0.5 μm thick is applied, which was producedexclusively with the Ti—Si sources. Alternately, a thicker AlCrN coverlayer can be applied here. All layers were deposited in an atmosphere ofpure nitrogen at a pressure of around 3 pa and a negative substratepreliminary voltage of roughly 50 volts. Basically the process pressurein each of these steps can be set in a range from 0.5 to around 8 pa,but preferably between 0.8 and 5 Pa, whereby the atmosphere can beeither pure nitrogen or a mixture of nitrogen and an inert gas, likeargon, for nitride layers, or a mixture of nitrogen and a gas containingcarbon, which can be mixed with an inert gas if necessary can be usedfor carbonitride layers. Accordingly, oxygen or a gas containing boroncan be mixed in, as is known, for the deposition of layers containingoxygen or boron.

Table 1 shows the composition of the target, the crystal structure ofthe layer and the adhesion. Table 2 summarizes the process parameters,such as the target capacity, negative substrate preliminary voltage,process pressure and temperature.

According to the invention, workpieces are distinguished by the factthat a cubic (Al_(y)Cr_(1-y))X layer is deposited with X=N or CN, butpreferably N, and 0.2≦y≦0.7, preferably 0.3≦y≦0.5 alternating with acubic (TizSi_(1-z))X layer with X=N or CN, but preferably N, and0.99≧z≧0.7, preferably 0.97≧z≧0.85 (see FIG. 1 a), whereby at least onelayer stack and at least one additional (Al_(y)Cr_(1-y))X or(Ti_(z)Si_(1-z))X layer is applied. The structure of the layers ismicrocrystalline in both layers with an average grain size of approx.5-150 nm, but preferably from approximately 10-120 nm. One advantage ofthe coating is the additional intermediate layers between the pure(Al_(y)Cr_(1-y))X and (Ti_(z)Si_(1-z))X layers, in which all coatingsources run and thus an (Al_(y)Cr_(1-y)Ti_(z)Si_(1-z))X layer isdeposited (see FIG. 1 b). These intermediate layers can, if necessary,depending on the sequence or composition and properties of theindividual layer systems, bring about improved adhesion between theindividual layers. Due to the geometric target arrangement within thecoating system, because of the rotation of the workpiece during thedeposition of this intermediate layer, a multilayer structure with veryfine layers is also deposited, since as before individual Al—Cr-basedand Ti—Si-based targets are used for the coating. The width of theindividual layers within this intermediate layer is in the range ofseveral nanometers.

Another way of designing the desired multilayer system, can be byperiodically turning the coating sources on and off similarly to FIG. 1c. Here, the coating sources for a coating material run during the wholedeposition process, while the coating sources with the second coatingmaterial are switched on periodically. In this case, an additionalmultilayer structure, as mentioned above, can be produced while the arcsources operate together.

The method in the invention is characterized by the fact that a processis chosen in order to deposit the layer stack described above. Themultilayer structure is achieved by purposely turning the coatingsources on and off. The multilayer substructure is maintained inaddition by rotating or moving the workpieces being coated within thecoating system.

Example 1 describes coatings with a defined number of layers or packetsof layers, whereby a layer stack consists of a sequence of AlCrTiSiNlayers followed by a layer of TiSiN, AlCrTiSiN and AlCrN. It is easy tosee that compared to the layer tested in Experiment No. 1, which wasdeposited according to the state of the art, an improvement in tool lifecan be achieved with the coating in the invention. It is also clear thatthe optimal layer thickness of the individual layers made ofAl_(y)Cr_(1-y)N and Ti_(z)Si_(1-z)N is important for the necessaryincrease in tool life. This layer thickness for Al_(y)Cr_(1-y)N isbetween 75 nm and 200 nm, preferably 120 nm to 170 nm, and forTi_(z)Si_(1-z)N between 50 and 150 nm, preferably between 70 to 120 nm.In this example, these layer thicknesses were altered over the coatingtime so that for all experiments, a comparable layer thickness ofroughly 4 μm could be achieved. For these experiments, a layer designwas chosen like the one described in FIG. 1 b. The layers, in which allcoating sources were used, were not changed for the respectiveexperiments and yielded an individual layer thickness of around 20±10nm, respectively.

Basically, completely different workpieces can be coated advantageouslywith these kinds of Al_(y)Cr_(1-y)N/Ti_(z)Si_(1-z)N multilayer coatings.Examples of this are cutting tools like milling cutters, hob cutters,spherical head cutters, planar and profile cutters and drills, taps,shaving dies, reamers and indexable inserts for lathe and mill work andforming tools like stamps, dies, drawing dies, knockout cores or threadformers. Also injection-molding tools, for example for metalinjection-molding alloys, synthetic resins or thermoplastics, especiallyinjection-molding tools like those used for producing plastic moldedparts or data carriers like CDs, DVDs et al., can be protectedadvantageously with such layers. Although better results are not alwaysachieved by the coatings in the inventions for all applications ondifferent tools, much higher wear resistance can be achieved, at leaston certain applications and in the examples listed than with thecoatings known in the past.

In addition, because of the behavior of Al_(y)Cr_(1-y)N/Ti_(z)Si_(1-z)Xmultilayer coatings, which is similar in principle, an improvement inwear behavior can be expected when target compositions and coatingparameters in the following layer systems are chosen so that X=N, C, B,CN, BN, CBN, NO, CO, BO, CNO, BNO and CBNO, but preferably N and CN and0.2≦y≦0.7, preferably 0.40≦y≦0.68 and 0.99≧z≧0.7, preferably0.95≧z≧0.85.

One way of improving the coating properties ofAl_(y)Cr_(1-y)N/Ti_(z)Si_(1-z)N multilayer coatings consists of alloyingother chemical elements from one or more groups of Groups IVb, Vb and/orVIb of the Periodic Table of the Elements, or silicon. It can beespecially advantageous to alloy with the layer stack of theAl_(y)Cr_(1-y-m)M_(m)N layer, with 0≦m≦0.25, preferably with 0≦m≦0.15.The elements for M=W, V, Mo, Nb and Si have proven particularlyadvantageous (see Example No. 5).

Another way of improving the properties of the layer system is to put anextra sliding layer on the layer stack or on the cover layer closing thehard coating on the outside. The sliding coating system can be made ofat least one metal or a carbide of at least one metal and dispersecarbon, MeC/C, whereby the metal is a metal from the Group IVb, Vband/or VIb and/or silicon. For example, a WC/C cover layer with ahardness that can be set between 1000 and 1500 HV that has excellentintake properties is especially suitable for this. CrC/C coatings alsohave similar behavior with a somewhat higher friction coefficient.

With such coated deep-hole drills, after a bore hole was produced, itwas possible to detect additional intake smoothness of the chipsurfaces, which has only be achieved to date by expensive mechanicalmachining. This results in an improvement in chip transport along thechip groove and minimization of friction torque during the drillingprocess. Such properties are also of interest particularly for componentapplications with sliding, rubbing or rolling stresses, especially whenthere is a lack of lubrication or when they run dry, or if an uncoatedcounter body must be protected at the same time. Other ways of making asealing sliding coating are metal-free diamond-like carbon coatings, orMoS_(x), WS_(x) or MoS_(x) or MoW_(x) layers containing titanium.

The sliding layer can be applied, as mentioned, directly to themultilayer system or after another adhesive layer is applied, in orderto achieve the best possible adhesion of the layer composite. Theadhesive layer can be designed to be made of metal, nitride, carbide,carbonitride or as a gradient layer.

For example, WC/C or CrC/C layers can be produced, after applying asputtered or arced Cr or Ti adhesive layer, advantageously by sputteringa WC target while adding a gas containing carbon. Here, the percentageof gas containing carbon is increased over time to achieve a largerpercentage of free carbon in the layer.

OTHER ADVANTAGEOUS EFFECTS OF THE INVENTION

The following will show advantageous applications of the invention, asexamples, using different cutting operations.

EXAMPLE 1 Drills with Inner-Cooled HM Drill Bits of Structural Steel

Tool: Hard metal drill with cooling ducts Diameter D = 6.8 mm Workpiece:Structural steel DIN 1.1191 (Ck45) Drilling parameters: Cutting speedv_(c) = 120 m/min Tooth feed f_(z) = 0.2 mm/rotation Hole depth z = 34mm (5 × D) Cooling: 5% emulsion Process: blind hole Wear criterion:Corner wear VB = 0.2 mm Tool life expressed Layer in units of length ofthickness path traversed** Experiment No. [μm] [m] 1 AlCrN + TiSiN 3.954.3 2 AlCrN + 2 × layer stack 1* + TiSiN 4.2 43.9 3 AlCrN + 4 × layerstack 1* + TiSiN 3.9 65.2 4 AlCrN + 8 × layer stack 1* + TiSiN 4.0 76.25 AlCrN + 12 × layer stack 1* + TiSiN 4.0 54.3 6 AlCrN + 15 × layerstack 1* + TiSiN 3.9 43.9 *A (1×) coating stack corresponds to aone-time sequence of “AlCrTiSiN + TiSiN + AlCrTiSiN + AlCrN.” **In whichthe width of the wear land was VB = 0.2 mm.

Example 1 shows a comparison of the tool lives of coated HM drills, inwhich a different number of coating stacks were applied with the sameadhesive layer, namely AlCrN and a cover layer, namely TiSiN. Thecoating time of the TiSiN and AlCrN layers was adjusted so that in theend, the total thicknesses of the layers were comparable. An optimumtotal tool life was found in Experiment No. 4 with a total number of 37layers, which shows a clear improvement over the state of the art fromExperiment No. 1.

EXAMPLE 2 Drills with Inner-Cooled HM Drills of Structural Steel

Tool: Hard metal drill with cooling ducts Diameter D = 6.8 mm Workpiece:Structural steel DIN 1.1191 (Ck45) Drilling parameters: Cutting speedv_(c) = 120 m/min. Tooth feed f_(z) = 0.2 mm/rotation Hole depth z = 34mm (5 × D) Cooling: 5% emulsion Process: Blind hole Wear criterion:Corner wear VB = 0.2 mm Tool life expressed in length of path traversedExperiment No. with VB = 0.2 mm in meters  6 (TiAlN/TiN multilayer) 32.3 8 (TiAlN monolayer) 32.3  9 (AlCrN monolayer) 65.9 10 AlCrN + 8 × layerstack 1* + TiSiN 76.2

Example 2 shows a comparison of the tool lives of coated HM drill bits.Here, an improvement in tool life was also able to be achieved with theAlCrN/TiSiN multilayer compared to hard coatings of TiAlN/TiN multilayerand TiAlN monolayer coatings used industrially.

EXAMPLE 3 Drills with Outer-Cooled HM Drill Bits of Structural Steel

Tool: Hard metal drill with cooling ducts Diameter D = 6.8 mm Workpiece:Structural steel DIN 1.1191 (Ck45) Drilling parameters: Cutting speedv_(c) = 120 m/min. Tooth feed f_(z) = 0.2 mm/rotation Hole depth z =23.8 mm (3.5 × D) Cooling: 5% emulsion Process: Blind hole Wearcriterion: Corner wear VB = 0.15 mm Tool life expressed in length ofpath traversed Experiment No. with VB = 0.15 mm in meters 11 (TiAlN/TiNmultilayer) 46.1 12 (TiAlN monolayer) 42.3 13 (AlCrN monolayer) 22.6 14AlCrN + 8 × layer stack 1* + TiSiN 61.5

Example 3 shows a comparison of the tool lives of coated HM drill bits.Here, an improvement in tool life was also able to be achieved with theAlCrN/TiSiN multilayer compared to hard TiAlN-based coatings usedindustrially.

EXAMPLE 4 Drills with Inner-Cooled HM Drill Bits of Cast Iron (GGG-50)

Tool: Hard metal drill with cooling ducts Diameter D = 6.8 mm Workpiece:Cast iron with spherical graphite GGG50 Drilling parameters: Cuttingspeed v_(c) = 200 m/min. Tooth feed f_(z) = 0.3 mm/rotation Hole depth z= 34 mm (5 × D) Cooling: 5% emulsion Process: Blind hole Wear criterion:Corner wear VB = 0.1 mm Tool life expressed in length of path traversedExperiment No. with VB = 0.1 mm in meters 15 (TiAlN/TiN multilayer) 57.116 (TiAlN monolayer) 142.8 17 (AlCrN monolayer) 185.6 18 AlCrN + 8 ×layer stack 1* + TiSiN 199.9

Example 4 shows a comparison of the tool lives of coated HM drill bits.Here, an improvement in tool life was also able to be achieved with theAlCrN/TiSiN multilayer coating compared to hard layers of TiAlN/TiNmultilayer coating and TiAlN monolayer coatings used industrially.

EXAMPLE 5 Drills with Inner-Cooled HM Drill Bits of Structural Steel

Tool: Hard metal drill with cooling ducts Diameter D = 6.8 mm Workpiece:Structural Steel DIN 1.1191 (Ck45) Drilling parameters: Cutting speedv_(c) = 120 m/min. Tooth feed f_(z) = 0.2 mm/rotation Hole depth z = 34mm (5 × D) Cooling: 5% emulsion Process: Blind hole Wear criterion:Corner wear VB = 0.2 mm Layer Tool life expressed Al Cr M thickness inlength of path traversed Experiment No. at % at % at % [μm] with VB =0.2 mm in meters 19 AlCrWN + 8 × layer stack 2* + TiSiN 70 28 2 3.8 65.820 AlCrWN + 8 × layer stack 2* + TiSiN 70 25 5 3.4 59.3 21 AlCrNbN + 8 ×layer stack 2* + TiSiN 70 25 5 3.8 57.8 22 AlCrMoN + 8 × layer stack2* + TiSiN 70 25 5 4.8 61.2 23 AlCrVN + 8 × layer stack 2* + TiSiN 70 255 4.2 68.0 24 AlCrSiN + 8 × layer stack 2* + TiSiN 70 25 5 4.0 54.4 *A(1×) layer stack 2* corresponds to a one-time coating sequence of“AlCrMTiSiN + TiSiN + AlCrMTiSiN + AlCrMN,” wherein M stands for one ofthe elements W, Nb, Mo V or Si.

Example 5 shows a comparison of the tool lives of HM drills coatedaccording to the invention on which multilayer systems with differentchemical compositions, but the same cover layer (TiSiN) were deposited.As a chemical composition, the target composition was varied, wherein Alwas kept constant, and Cr was partly replaced by a third element. Theprocess parameters for layer deposition were kept equal as in the otherexperiments.

Another way of producing a corresponding layer stack is when, as in FIG.1 c, either the AlCr or AlCrM sources or the TiSi source or sources areoperated constantly and the other source or sources are turned on asneeded. In particular with constant operation of the above-mentioned 4AlCr or AlCrM sources, the deposition rate can be increased, and thefollowing layer system can be deposited, for example:

-   -   one (AlCrTiSi)X mixed layer    -   followed by another (Al_(y)Cr_(1-y))X layer    -   followed by another (AlCrTiSi)X mixed layer    -   followed by another (Al_(y)Cr_(1-y))X layer.

DESCRIPTION OF FIGURES

FIG. 1 shows different layer variations. FIGS. 1 a-c discuss threevariations of how a multilayer coating can be made.

FIG. 1 a shows a sequence of layers with sharp transitions. A layersystem (2) is deposited directly on a second layer system (1). Thisprocess is repeated until the desired total layer thickness is reached.A cover layer (3) with higher thicknesses can be deposited as the lastlayer.

In FIG. 1 b, mixed layers (4) in which both layer systems are appliedsimultaneously are deposited between the individual layers. The mixedlayer can be made either thin as a sliding transitional layer or thickerwith an area where the composition of the layer is constant. Such alayer can have the following composition, for example: Al=40.7 at %,Cr=21.2 at %, Ti=32.8 at % and Si=5.3 at %. This composition comes aboutwhen AlCr targets with a composition of Al=70 at % and Cr=30 at % andTiSi targets with a composition of Ti=85 at % and Si=15 at % are usedsimultaneously. In general, the composition of a mixed layer with aconstant composition is advantageously set in the following range:(Al_(1-a-b-c)Cr_(a)Ti_(b)Si_(c))Xwhere 0.18≦a≦0.48; 0.28≦b≦0.4; 0.004≦c≦0.12. The aluminum content isadvantageously kept at over 10 at %. If other elements are added, asmentioned above, to achieve a corresponding effect, depending on theelement, a minimum concentration of 0.5 to 1 atom percentage and amaximum concentration of 15% to 25% are added.

In FIG. 1 c, a multilayer coating is deposited by applying a layersystem (5) during the whole coating time, and the second layer system isperiodically mixed in with it by turning on the corresponding coatingsource.

FIG. 2 shows the design of the layer packet in FIG. 1 in an alteredview.

TABLE 1 Composition of Target Target 1 Layer Crystal Al Cr Target 2Thickness Experiment Structure at % at % M at % Ti at % Si at % [μm]Adhesion A B1 70 30 — 85 15 4.0 HF1 B B1 70 28 W = 2 85 15 3.8 HF1 C B170 25 2 = 5 85 15 3.4 HF1 D B1 70 25 Nb = 5 85 15 3.8 HF1 E B1 70 25 V =5 85 15 4.8 HF1 F B1 70 25 Mo = 5 85 15 4.2 HF1 G B1 70 25 Si = 5 85 154.0 HF1

TABLE 2 P_(Target)Al—Cr-M P_(Target)Ti—Si U_(Substrate) P_(N2) Temp.Experiment [kW] [kW] [V] [Pa] [° C.] A 3 3 −50 3 500 B 3 3 −50 3 500 C 33 −50 3 500 D 3 3 −50 3 500 E 3 3 −50 3 500 F 3 3 −50 3 500 G 3 3 −50 3500

1. A method of providing a hard coating on a workpiece, comprising: a)positioning the workpiece in a coating system adjacent at least oneTiSiX target and at least one AlCrX target, each of said targets havingan associated cathodic arc source, wherein X is selected from the groupconsisting of N, C, B, CN, BN, CBN, NO, CO, BO, CNO, BNO, and CBNO; b)rotating the workpiece; c) applying a biasing voltage to said workpiece;and d) selective operating said cathodic arc sources to deposit amultilayer coating onto the workpiece, said multilayer coatingcomprising: at least one layer selected from the group consisting of: an(Al_(y)Cr_(1-y))X layer, wherein 0.2≦y≦0.7 and X is selected from thegroup consisting of N, C, B, CN, BN, CBN, NO, CO, BO, CNO, BNO, andCBNO, and a (Ti_(z)Si_(1-z))X layer, wherein 0.99≧z≧0.7, and at leastone layer stack comprising the following layers: one (AlCrTiSi)X mixedlayer followed by another (Ti_(z)Si_(1-z))X layer followed by another(AlCrTiSi)X mixed layer followed by another (Al_(y)Cr_(1-y))X layer,wherein X, y and z are as previously defined.
 2. The method of claim 1,said coating system comprising six cathodic arc sources, two TiSitargets being associated with two of said cathodic arc sources, and fourAlCrX targets being associated with the remaining four of said arcsources, said arc sources and targets being arranged in a patter aroundthe workpiece with the workpiece disposed in the center.
 3. The methodof claim 1, said workpiece being brought to a temperature ofapproximately 500° C. and its surface cleaned by bombardment of Ar ionsin an Ar atmosphere at a pressure of 0.2 Pa prior to said step (d). 4.The method of claim 1, said step (d) being carried out under an inertatmosphere at a pressure of 0.5 to 8 Pa.
 5. The method of claim 4, saidinert atmosphere comprising an inert gas that is selected to correspondto the composition of the layer being applied to the workpiece at agiven time.
 6. The method of claim 1, wherein the following depositionsteps are carried out in sequence to deposit successive layers onto saidworkpiece: i) deposition of an AlCrX adhesive layer having a thicknessof approximately 0.2 microns; ii) operating the cathodic arc sourcesassociated with all of said targets together to deposit a mixedAlCrX/TiSiX layer; iii) turning off only the cathodic arc sourcesassociated with said at least one AlCrX target to deposit a pure TiSiXlayer; iv) reactivating the cathodic arc sources associated with said atleast one AlCrX target to again deposit a mixed AlCrX/TiSiX layer; andv) turning off the cathodic arc sources associated with said at leastone TiSi target to deposit a pure AlCrX layer.
 7. The method of claim 6,said steps (i)-(v) being repeated in sequence to deposit a plurality ofstacks of said successive layers onto said workpiece.
 8. The method ofclaim 7, wherein after said plurality of stacks have been deposited, apure TiSiX layer having a thickness of approximately 0.5 microns isdeposited thereover.
 9. The method of claim 6, wherein X=N.
 10. Themethod of claim 1, characterized by the fact that the at least one(Al_(y)Cr_(1-y))X layer, the other (Al_(y)Cr_(1-y))X layer and the(AlCrTiSi)X mixed layers contain at least one other element from GroupIVb, Vb and/or VIb of the Periodic Table of the Elements, or silicon.11. The method of claim 10, characterized by the fact that the at leastone (Al_(y)Cr_(1-y))X layer and the other (Al_(y)Cr_(1-y))X layercontain 0.5 to 25 atom % of the other element or silicon, setting theconcentration of the elements and of the silicon in the other (AlCrTiSi)X mixed layers.
 12. The method of claim 1, characterized by the factthat the layers in the layer stack have the following thickness:Al_(y)Cr_(1-y)N layer between 75 nm and 200 nm Ti_(z)Si_(1-z)N layerbetween 50 and 150 nm (AlCrTiSi)X mixed layer 20±10 nm.
 13. The methodof claim 1, characterized by the fact that the coating includes severallayer stacks in a row.
 14. The method of claim 13, characterized by thefact that the coating contains 4, 8 or 12 layer stacks.
 15. The methodof claim 1, characterized by the fact that at least one(Al_(y)Cr_(1-y))X layer is deposited directly on the workpiece or on anadhesive layer.
 16. The method of claim 1, characterized by the factthat a (Al_(y)Cr_(1-y))X cover layer or a (Ti_(z)Si_(1-z))X layer formsthe outer last layer of the hard coating.
 17. The method of 1,characterized by the fact that an additional sliding layer is depositedon the hard coating.
 18. A method of providing a hard coating on aworkpiece, comprising: a) positioning the workpiece in a coating systemadjacent at least one TiSiX target and at least one AlCrX target, eachof said targets having an associated cathodic arc source, wherein X isselected from the group consisting of N, C, B, CN, BN, CBN, NO, CO, BO,CNO, BNO, and CBNO; b) rotating the workpiece; c) applying a biasingvoltage to said workpiece; and d) selective operating said cathodic arcsources to deposit a multilayer coating onto the workpiece, saidmultilayer coating comprising: at least one layer selected from thegroup consisting of: an (Al_(y)Cr_(1-y))X layer, wherein 0.2≦y≦0.7 and Xis selected from the group consisting of N, C, B, CN, BN, CBN, NO, CO,BO, CNO, BNO, and CBNO, and a (Ti_(z)Si_(1-z))X layer, wherein0.99≧z≧0.7, and at least one layer stack comprising the followinglayers: one (AlCrTiSi)X mixed layer followed by another(Al_(y)Cr_(1-y))X layer followed by another (AlCrTiSi)X mixed layerfollowed by another (Al_(y)Cr_(1-y))X layer, wherein X, y and z are aspreviously defined.
 19. The method of claim 1, said workpiece comprisingby the fact that the workpiece is tool for machining, forming orcutting.
 20. The method of claim 1, said workpiece being a drill. 21.The method of claim 11, wherein X is selected from the group consistingof N and CN.
 22. The method of claim 1, wherein: X in said at least onelayer is N or CN, X in said (Ti_(z)Si_(1-z))X layer is N or CN, and0.95≧z≧0.85.
 23. The method of claim 1, wherein X is N or CN in everyrecited layer.
 24. The method of claim 1, wherein 0.3≦y≦0.5 and0.97≧z≧0.85.